Surge arrester

ABSTRACT

A surge arrester incorporates conventional valve block means and gap structure connected in series and disposed within a water tight housing of elastomeric material. The ground and line terminals protrude through openings in the housing and are sealed thereto. One of the terminals extends through a pressure relieving cap which itself is sealed to the housing in water tight fashion and a stress relief element is interconnected with each terminal of the arrester and generally surrounds the adjacent portions of the gap structure and block means respectively.

United States Patent [191 Westrom SURGE ARRESTER Arthur C. Westrom, Stone Mountain, Ga.

Kearney National Inc., Atlanta, Ga.

Feb. 15, 1972 Inventor:

Assignee:

Filed:

App]. No.:

[52] [1.8. CI ..317/68, 3l3/DIG. 5, 315/36,

. 317/70 Int. Cl. ..H02h 9/06 Field of Search ..313/220,' 221 312,

313/317, DIG. 5; 315/36; 317/62, 68, 70

[ 5 6] References Cited UNITED STATES PATENTS 3,018,406 1/1962 Innis ..3 15/36 [451 Apr.10,1973

2,331,852 10/1943 Stoelting ..3l3/DIG.5 3,248,599 4/1966 Masuda ..3l5/36 Primary Examiner-James D. Trammell Attorney-Walter M. Rodgers [57 ABSTRACT 6 Claims, 5 Drawing Figures IM 5 1a 14 1/ z 2 I j 22 22 I 21 SURGE ARRESTER Conventional surge arresters ordinarily are housedwithin a porcelain enclosure which constitutes a hazard when failure of. the arrester occurs due to the rapid development of explosive pressures which may cause the housing to shatterexplosively thus endangering personnel and equipment. Furthermore porcelain housings are difficult to construct in a moisture tight fashion'because the brittle porcelain frequently cracks and because the seal between the housing and the live or grounded conducting parts is difficult to form and consistently maintain in a moisture tight condition. Lightning arresters mounted in a porcelain housing ordinarily become contaminated externally due to the accummulation of foreign matter thereon from the atmosphere. Such contamination tends to bring the ground plane closer to the interior spark gap thereby lowering the spark gap flashover characteristic. Porcelai'n housings also are difficult to shield and frequently such housing structures do not incorporate shielding elements of any type. The practical unavailability of an arrester which is constructed so as to overcome the above difficulties has been fully recognized by the Institute of Electrical and Electronics Engineers Power Engineering Society as well as by working groups of the Institute.

According 'to this invention, conventional lightning arrester gap structure and series connected valve blocks are housed within an enclosing housing formed of elastomeric material. Such housing structure may be rendered moisture tight by simply vulcanizing or otherwise sealing the arrester terminals where they extend through the housing in a moisture tight manner thereby to protect internal parts from water contamination and also from internal contamination by particles from the atmosphere. Of course the elastomeric housing does not shatter in case of arrester failure and hence such structure poses no hazard to personnel or to equipment. According to one facet of the invention, shielding elements are connected to the terminals of the arrester and, if desired, the shielding element which is connected to the energized terminal may be conveniently imbedded within the elastomeric housing and -in conjunction with the accompanying drawings in which FIG. 1 is a cross-sectional view of a lightning arrester constructed according to the invention;

FIG. 2A is a plan view of a pressure relief closure cap which forms a part of a closure for the bottom end of the arrester shown in FIG. 1;

FIG. 2B is a plan view of an end conducting plate which forms a part of a closure for the bottom end of the arrester shown in FIG. 1;

FIG. 3 is a schematic one-line diagram which illustrates the manner in which underground transformers are connected to an overhead line and which illustrates the manner in which an arrester constructed according to this invention may be used underground in an underground distribution system so as to afford protection for underground electric components such as transformers and the like; and in which FIG. 4 is a cross-sectional view of a lightning arrester constructed according to the principles of this invention and which represent a modification of the invention which is especially adapted for underground use,

the arrester itself being shown in conjunction with an elbow type connector for interconnecting the arrester with an energized terminal of the underground system.

In FIG. I the numeral designates a housing of elastomeric material constructed according to this in vention. The numeral 2 designates conventional gap structure while the numeral 3 is used to designate conventional valve blocks connected in series with gap structure 2,. Gap structure 2 and valve blocks 3 are connected in series in conventional fashion and a compression spring 4 is arranged to urge the gap structure and valve blocks downwardly and into secure contact with an apertured metallic closure plate 5 disposed at the bottom end of housing 1. A terminal stud 6 is formed integrally with closure plate 5 and a conventional clamping plate 7 and conducting washer 8 are held in place on terminal stud 6 by means of nut 9.

At the upper end of the arrester, a conductor 10 constitutes a shunt whereby the gap structure 2 is positively interconnected with top end closure plate 11 fonned integrally with terminal stud 12. A clamping plate 13 and an end washer 14 are held in place on terminal stud 12 by nut 14A. Interconnection with the energized line of an electric system is by way of a conductor C which is clamped between the washer 14 and the clamping plate 13 and held in secure engagement therewith by terminal nut 14A. Similarly the grounding conductor C for the arrester is held in place between clamping plate 7 and washer 8 by means of nut 9. The conductors C which connect the lightning arrester to the system and ground are shown in section in FIG. 1.

For the purpose of rendering the arrester moisture tight at the upper end thereof, the elastomeric housing 1 is vulcanized or otherwise sealed about terminal stud 12 at the aperture through which the terminal stud 12 extends. I

In order to render the arrester moisture tight at the bottom end, an initially separate closure cap 16 is vulcanized or otherwise secured by suitable adhesive at the opening formed in the bottom of housing 1 and the closure element 16 is provided with an opening 18 which is vulcanized or sealed in any suitable manner about the terminal stud 6 to render the lower end of the arrester moisture tight.

In order to relieve internal pressure which may be generated inside the housing 1 due to malfunction or failure of the gap structure 2 or of valve blocks 3, a plurality of weakened segments 19 are formed within closure cap 16. The cap 16 is constructed of rubber or of some other type of elastomeric material and the end conducting plate 5 is constructed in a manner virtually' closure element 16 and housing l' are constructed of rubber or other elastomeric material which is shatterproof.

In order to establish a fixed and adequate di-electric separating means which provides a constant magnitude of voltage distribution between line terminal 12 and the grounded terminal 6, a stress relieving shield 21 is imbedded within the upper portion of the elastomeric housing 1 and is electrically connected with the upper terminal 12. This shield preferably is substantially coextensive in an axial direction with the gap structure 2 and hence is arranged so that its lower end portion 22 is disposed at approximately the same level as the lower end 23 of gap structure 2. This stress relief element 21 mayconstitute conductive rubber or any other suitable conducting means.

Cooperating'with stress relieving element 21 is a lower stress relieving element'24 which is formed preferably of conductive rubber embedded within elastomeric housing 1 and which is electrically con- I nected at the aperture 25 in housing 1 with the periphery of metallic closure element5. Thus stress relief element 24 is maintained at ground potential when the arrester is in service. Stress relief element 24, as is apparent in FIG. 1, is' substantially coextensive axially with the arrester blocks 3 and the upper end portion 26 thereof is disposed at approximately the same level as the upper portion 27 of the upper valve block 3. These stress relief elements are-configured in contour'a'nd dimensions to limit the stress to the insulation therebetween to an acceptable value.

In view of the above description, it is apparent that the system voltage stress is applied between the lower portion 22 of stress relief element 21 and the upper portion 26 of stress relieving element 24. Furthermore since the stress relieving elements are completely shielded from atmosphere, the device is thus rendered free of di-electric weakening due to the accumulation of contaminants along the exterior surface of the housing because the device is constructed of such size that any practical accumulation of such contaminants along the exterior of the housing would never under practical conditions constitute a hazard to the proper functioning of the'device.

The device shownin FIGS. 1, 2A and-2B is primarily intended for use above ground while the arrangement of FIG. 4 is primarily intended for use in underground distribution systems such as are represented by the lower portion of the schematic diagram of FIG. 3, the upper portion thereof representing above ground conductors and components.

In FIG. 3 the numeral 28 designates an overhead above ground distribution conductor. The numerals 29 and 30 designate schematically represented lightning arresters'which are interconnected between overhead conductor 28 and ground and which serve to protect the conductor 28 and associated elements against overvoltage due to lightning.

In FIG. 3, the numerals 31 and 32 designate insulated transformers which are mounted underground. Fused terminator switch 33 and insulated conductor 35 constitute means along with conventional elbow 36 for.

connecting overhead conductor 28 with one terminal 37 of transformer 31 when switch 33 and a separable insulated connector or elbow 36 are in their closed circuit positions. When so connected, transformer 31 may be connected to the lightning arrester of FIG. 4 at the terminal 38. Of course elbow 39 is disconnected under these conditions. Transformer 31 is provided with'a conventional fuse 34 and transformer 32 is similarly provided with a fuse 41.

Transformer 32 may be interconnected with conductor 28 by means of fused terminator switch 40, insulated conductor 42 and elbow 43 when the switch 40 and elbow 43 are in closed circuit positions. Under such conditions, transformer 32 may be protected from lightning surges by connecting an arrester to the terminal 44 by means of a suitable elbow connector, it being understood that elbow connector 45 is in open circuit position during such conditions.

Both transformers 31 and 32 may be energized through switch 33 and conductor 35 as when elbows 36, 39 and 45 are closed and lightning protection may be afforded by simply connecting a lightning arrester to terminal 46 while elbow 43 is disconnected.

Since underground switching connections are ordinarily made by elbow connectors, it is deemed desirable to show in FIG. 4 a connector for underground application and such a connector is generally designated by the numeral 47 and is arranged inseries in FIG. 4 with an arrester constructed according to this invention and generally designated by the numeral 48.

The arrester 48 comprises an external shield 49 disposed about an insulating housing 50 of elastomeric material. The shield 49 is preferably constructed of conductive rubber material and is electrically connected at its lower end 51 with the outer periphery of closure plate 52 preferably constructed of rubber. Closure element 53 is constructed of conducting material and its integral terminal 54 extends through an opening formed in closure element 52. The terminal'54 and'the aperture formed in closure element 52 are vulcanized or otherwise sealed at the junction therebetween so as to render the structure water tight. In like fashion, the junction between external stress relief element 49 at the lower end 51 thereof and the outer periphery of the closure element 52 is vulcanized or otherwise arranged in a water tight manner.

Disposed within the elastomeric housing 50 is a conventional valve block structure 55 which is in electric contact with the conducting plate 53 and conventional gap structure 56 is arranged in series with the valve blocks 55.

The bottom terminal 57 is provided with a clamping bracket 58 and a terminal washer 59 which .are held in place by nut 60. Terminal 57 is interconnected with ground via a conductor C.

The upper end of the arrester 48 includes an upper conducting socket 61; which is in contact with the upper portion 56a of gap structure'56 and a conducting stud 62 in the form of a connector crimped onto conductor 63 and having a ball at its end is arranged to form a disjointable connection with conductor socket 61 whereby the arrester 48 may be connected or disconnected from the connector 47 as desired.

The underground residential distribution type of shielded conductor 63 having an insulating sheath 63a and a semi-conducting rubber sheath 64 is slipped into the elastomeric housing 48 in a water tight fashion and with the semi-conducting sheath 64 stripped back for adequate insulation between the surge arrester inner shield 49B and the outer surge arrester shield 4).

Connector 47 is provided with an external conducting shield 66 which extends thereabout and which firmly envelops the semi-conducting rubber sheath 64 and which is also connected by means of a conductor 67 and with the external stress relief shield 49, the conductor 67 being wound about the underground residential distribution cable sheath 64 as indicated at 68 and being connected with the shield 66 at 69 and with the shield 49 at 70.

The conductor 63 extends through the sheath 64 and at the upper end thereof is freed of insulating material 63a and is gripped by the contact sleeve 71 by crimping or any other suitable means, the shield 66 and contact sleeve 71 being insulated from each other by suitable insulating mater'ial72. Contact sleeve 71 is provided with a portion 73 of reduced size which portion extends into an aperture formed within contact body 74. The threaded portion 75 of conventional contact pin 76 is screwed into an internally threaded opening formed in contact body 74 and the'inner end 77 of the contact pin 76 engages the reduced portion 73 of the contact sleeve 71 and securely holds the parts in the positions shown in FIG. 4. Shield 78 of conducting rubber constitutes an inner shield for the contact sleeve 71, the contact body 74 and the right hand end of contact pin 76.

. In order to connect the lightning arrester of FIG. 4 to the terminal 38 forexample as shown in FIG. 3, it is simply necessary to ground the lower terminal 57 thereof by any suitable means and to plug the elbow connector 47 into electric contact with the terminal 38. Likewise the elbow 47 may be plugged into any other terminal such as 46, 44, 37 as may be desired for the particular service conditions.

From the above description, it is apparent that both modifications of the invention are constructed in a water tight fashion and hence serve to eliminate one of the major causes of lightning arrester failure namely the entry of undesired water into the arrester housing and the resultant interferences with the functioning of the internal valve blocks and gap structure. Furthermore, both arrangements are shatter proof in that 'means are provided for relieving pressure generated internally in a manner to preclude dangerous explosions. Furthermore the fact that the housings are constructed of elastomeric material virtually precludes any damage due to excess internal pressure since the elastomeric material is shatterproof. Since both arrangements are provided with stress relief elements and since the stress relieving element which is connected to the high voltage system is imbedded within the elastomeric housing structure and thus protected from external contamination from the atmosphere, it is possible to provide an arrangement wherein accumulation on the exterior of the housing is ineffective to interfere with the proper dielectric strength of the arrester between ground and the energized system due to the mherent design of the by the upper stress relieving element in reference to ground due to the fact that the stress relieving elements are generally cylindrical in shape and hence devoid of sharp points on which high stress voltage or corona conditions could develop.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

' l. A surge arrester comprising a housing of elastomeric material, valve block means and gap structure connected in series and disposed within said housing, and conducting terminals connected to said valve block means and to said gap structure respectively and extending through apertures in said housing to form external connections for the arrester, said housing being liquid tight and being effective to prevent contamination of said gap structure and of said valve block means by foreign substances from outside said housing, one of said terminals being disposed in an aperture formed in an initially separate pressure relieving cap formed at least in part of elastomeric material and constituting a part of a wall of said housing.

2. An arrester according to claim 1 wherein said pressure relieving cap is formed with weakened sections for facilitating relief of pressure within said housing which is in excess of a predetermined magnitude.

3. An arrester according to claim 2 wherein pressure in excess of a predetermined magnitude causes saidcap to stretch and expand initially and subsequently to rupture.

4. An arrester according to claim 1 wherein one of said terminals comprises a pair of series conductors which are disconnectable from each other and whose cooperating contact portions when connected are disposed within said housing,.

5. An arrester according to claim 1 wherein said one terminal is sealed to said cap at the aperture therein and wherein said cap is secured to said housing via a water tight seal.

6. A surge arrester comprising a housing of elastomeric material, valve block means and gap structure connected in series and disposed within said housing, conducting terminals connected to said valve block means and to said gap structure respectively and extending through apertures in said housing to form external connections for arrester, said housing being liquid tight and being effective to prevent contamination of said gap structure and of said valve block means by foreign substances from outside said housing, and a conducting stress relief element connected to each of said terminals, said stress relief elements constituting capacitance means in parallel with said valve block means and said gap structure, one of said stress relief elements being disposed about and being substantially coextensive axially with said valve block means and the other of said stress relief elements being disposed about and being substantially coextensive axially with said gap structure. 

1. A surge arrester comprising a housing of elastomeric material, valve block means and gap structure connected in series and disposed within said housing, and conducting terminals connected to said valve block means and to said gap structure respectively and extending through apertures in said housing to form external connections for the arrester, said housing being liquid tight and being effective to prevent contamination of said gap structure and of said valve block means by foreign substances from outside said housing, one of said terminals being disposed in an aperture formed in an initially separate pressure relieving cap formed at least in part of elastomeric material and constituting a part of a wall of said housing.
 2. An arrester according to claim 1 wherein said pressure relieving cap is formed with weakened sections for facilitating relief of pressure within said housing which is in excess of a predetermined magnitude.
 3. An arrester according to claim 2 wherein pressure in excess of a predetermined magnitude causes said cap to stretch and expand initially and subsequently to rupture.
 4. An arrester according to claim 1 wherein one of said terminals comprises a pair of series conductors which are disconnectable from each other and whose cooperating contact portions when connected are disposed within said housing,.
 5. An arrester according to claim 1 wherein said one terminal is sealed to said cap at the aperture therein and wherein said cap is secured to said housing via a water tight seal.
 6. A surge arrester comprising a housing of elastomeric material, valve block means and gap structure connected in series and disposed within said housing, conducting terminals connecteD to said valve block means and to said gap structure respectively and extending through apertures in said housing to form external connections for arrester, said housing being liquid tight and being effective to prevent contamination of said gap structure and of said valve block means by foreign substances from outside said housing, and a conducting stress relief element connected to each of said terminals, said stress relief elements constituting capacitance means in parallel with said valve block means and said gap structure, one of said stress relief elements being disposed about and being substantially coextensive axially with said valve block means and the other of said stress relief elements being disposed about and being substantially coextensive axially with said gap structure. 